Energy

A. Energy Definition

The ability to do work.

What is Work?

B. Two Types of Energy

a. Kinetic Energy- the energy an object has due to its motion.

b. Potential Energy- energy that is stored in an object due to its position.

Example: a rolling ball.

Example: a bow and arrow.

Example: a battery.

Identify one form of potential energy and one form of kinetic energy.

C. Calculating Energy

a. Kinetic Energy =

Mass X Velocity2

2

K.E. = mv2

2

b. Units –mass= kilograms (kg)velocity = meters per second (m/s)

K.E. = Joules

c. Practice Problemsi. An 80 kg man is jogging at a velocity of

4 m/s. What is his kinetic energy?

K.E. = mv2

2

K.E. = 80 kg X (4 m/s)2

2K.E. = 80 kg X 16 m/s 2

K.E. = 640 J

ii. A 40 kg boy is jogging at a velocity of

4 m/s. What is his kinetic energy?

K.E. = mv2

2

K.E. = 40 kg X (4 m/s)2

2K.E. = 40 kg X 16 m/s 2

K.E. = 320 J

iii. A 40 kg boy is jogging at a velocity of 2 m/s. What is his kinetic

energy?

K.E. = mv2

2

K.E. = 40 kg X (2 m/s)2

2K.E. = 40 kg X 4 m/s 2

K.E. = 80 J

Potential Energy

d. Calculating Potential Energy

Gravitational Potential energy = weight x height

P.E. = w x h

e. Potential Energy Units

Weight = Newton’s (N)

Height = meters (m)

P.E. = Joules (J)

f. Practice Problems

i. A 22 Newton book is placed on a shelf that is 0.86 meters high.

P.E. = w x h

P.E. = 22 N x 0.86 m

P.E. = 18.92 J

ii. A 22 Newton book is placed on a shelf that is 1.86 meters high.

P.E. = w x h

P.E. = 22 N x 1.86 m

P.E. = 40.92 J

How much Potential Energy does the racquet ball have at 100 cm and 50 cm? The racquet ball weighs 4.2 N.

What is the relationship between bounce height and potential energy?